1. Field of Invention
This invention pertains to a device which relies on a piezoelectric material to produce a spatial displacement in response to an electrical input.
2. Description of Prior Art
Actuators are devices which can translate electrical energy to mechanical energy and sensors are devices which can translate mechanical energy to electrical energy.
The devices based on piezoelectric material operate on the principle of applying an electrical field to a block of the material wherein the material produces a proportional displacement, with the proportionality characterized by the piezoelectric activity coefficients d.sub.33, d.sub.31 and others. The first digit denotes the poling direction, whereas the second digit denotes the displacement direction. So if a vertically disposed block of piezoelectric material is poled vertically and the displacement utilized is also vertical, then the piezoelectric activity coefficient for this mode of operation is d.sub.33. If the vertically disposed block is poled horizontally through its thickness and displacement is sensed in the vertical direction, the appropriate piezoelectric activity coefficient for this mode of operation is d.sub.31. The magnitude of d.sub.33 in the piezoelectric material lead zirconate titanate (PZT) is equal to approximately 2.5 times that of its d.sub.31 coefficient.
The prior art actuators, relevant here, are used in applications varying from vibration damping to noise suppression to the shaping of air foils, in the approximate frequency range of less than 1 Hz to 10,000 Hz.
The prior art actuators operate on the principle that the application of a driving voltage produces a lengthwise displacement which is proportional to the length of the actuator. Thus, the longer the actuator, the greater the displacement. For instance, a driving voltage of 1000 volts applied to a 100 mm long actuator can produce a displacement of approximately 0.05 mm.
The problem with a 100 mm-long actuator is that it may be too long for an intended application. This invention makes it possible to reduce the external length of the actuator to the desired value and yet obtain the displacement obtained, for example, by a 100 mm long, one-piece actuator.